Novel photographic product and process



United States Patent 3,451,814 NOVEL PHOTOGRAPHIC PRODUCT AND PROCESS Edwin H. Land, Cambridge, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware No Drawing. Filed July 25, 1963, Ser. No. 297,658

Int. Cl. G03c 5/54 US. C]. 96-29 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to photography and, more particularly, to novel photographic products and processes for preparing visible images.

One object of the invention, therefore, is to provide a novel photographic system for preparing visible images.

Another object is to provide a novel one-step system for preparing negative images.

Still another object is to provide a novel one-step systern for preparing a printing master useful in photomechanical reproduction to obtain either positive or negative print copies of the original subject matter.

A further object is to provide a novel photographic system wherein the aforementioned objectives are accomplished by developing an exposed photosensitive element, as a product of development forming an imagewise distribution of constituents which are capable of affecting the optical density, e.g., the light-absorption or light-reflection characteristics, of a superposed sheet material, and transferring said imagewise distribution of constituents to said superposed sheet material to form a visible image.

Yet another object is to provide a novel photographic system wherein an exposed photosensitive element is developed to form, as a product of development, an imagewise distribution of constituents which are capable of rendering a normally opaque sheet material light-transmittant, and transferring at least part of said imagewise distribution of constituents, by imbibition, to said sheet material whereby to render said sheet material light-transmittant in areas corresponding to said imagewise distribution of transferred constituents.

A still further object is to provide a novel photographic system utilizing the principle of selective exhaustion of alkali from an aqueous alkaline processing solution to obtain a visible image.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

It is of course well known to prepare photographic images by diffusion transfer processes. Generally speaking, such processes include the steps of developing an exposed photosensitive element and transferring an imagewise distribution of image-forming constituents, by imbibition, to a superposed layer adapted to receive the image. The image-forming constituents are deposited on this layer where they either form the visible image per se or react with some material on the layer to form a color image or a change in color as a product of this reaction.

While the present invention is similar in some aspects to diffusion transfer processes of the foregoing description, it differs materially in that the visible image is not formed by depositing an imagewise distribution of ingredients which themselves form the visible image. Rather, the present invention utilizes an imagewise distribution of ingredients which alter the optical properties of a layer of material to provide an image thereon.

According to the present invention, visible images of good contrast and density are obtained by developing an exposed photosensitive element and, as a function of development, forming an imagewise distribution of constituents which are capable of altering the optical density, e.g., the light-absorption or lightreflection characteristics, of a superposed sheet material, and transferring at least a portion of this imagewise distribution, by imbibition, to the sheet material to produce an imagewise alteration of the optical density of the sheet material.

In one aspect of the present invention, a visible image is formed by developing an exposed photosensitive element to form, as a product of development, an imagewise distribution of constituents which are capable of rendering a normally opaque sheet material light-transmittant, and transferring at least a portion of said imagewise dis tribution of constituents, by imbibition, to said sheet material while it is in superposed relationship with said photosensitive element, whereby to render said sheet material light-transmittant in areas corresponding to said imagewise distribution of transferred constituents.

In the preferred embodiment of the present invention, use is made of the selective exhaustion. of alkali from an aqueous alkaline processing solution, as a function of development, and the transfer of unexhausted alkali to a normally reflective layer of a suitable metal in order to form the visible image.

It has heretofore been known that when an exposed photosensitive element comprising a silver halide emulsion is developed with an aqueous alkaline processing solution, the alkali may be substantially completely reacted, i.e., exhausted, in fully developed areas of the silver halide emulsion, partly exhausted in partially developed areas and substantially unreacted in undeveloped areas. Diffusion transfer processes utilizing this principle of selective exhaustion of alkali to form a transfer image are also known in the art. As an example of such processes, mention may be made of US. Patent No. 2,647,055 issued to Edwin H. Land. However, as far as is known, the principle of selective exhaustion of alkali has never been employed in photographic processes such as are contemplated by the preferred embodiment of the present invention.

It has now been found that, if an aqueous alkaline processing solution is spread between an exposed silver halide emulsion and a superposed sheet material comprising a relatively thin reflective layer of a suitable metal, alkali is exhausted in fully developed areas in the manner heretofore known in the art and the unexihausted alkali in the processing solution contacts the layer of metal where it alters the optical characteristics of the layer from lightreflective to light-transmittant to provide a negative transparency. The alteration of the optical properties from O light-reflective to light-transmittant is at least in part an etching of the metal sheet material by the alkali.

Accordingly, as used herein and in the appended claims, the description of the reflective layer as relatively thin connotes a layer thin enough so as to be capable of being rendered at least translucent by the imagewise distribution of unexhausted alkali in the processing composition. It will be appreciated that the particular thickness of the reflective layer may vary and will be dependent in part upon the ability of the amount of alkali present to react with the metal to accomplish the desired amount of etching and will be dependent in part upon the transmission density of the reflective metal layer. However, by way of illustration only, a typical relatively thin reflective layer of aluminum may be on the order of 45 micrograms/sq. inch or have a resistivity on the order of 1.6 ohms/ sq. centimeter.

While various metals may be employed in the practice of this embodiment of the invention, particularly good results have been obtained with aluminum. The optical density of the aluminum reflective layer may vary from about 0.75 to about 3.5, although best results are obtained where the reflective layer has an optical density of 2.20 to 2.60. Preferably, the aluminum is applied as a reflective layer on a suitable transparent support by vacuum deposition. This method of depositing a reflective surface of a metal on a support is well known in the art and per se comprises no part of the present invention.

The light-sensitive material employed in the practice of the preferred embodiment of the invention may be any of the silver halide emulsions customarily employed in the art.

The developing composition employed includes an aqueous alkaline solution of a silver halide developing agent. Best results are obtained by employing a fastacting developing agent, e.g., a developing agent which rapidly develops exposed silver halide, thereby rapidly exhausting alkali in fully developed areas. As an example of such developing agents, mention may be made of 4,6-diaminoortho cresol, amidol, triaminophenol, etc. The developing composition preferably but not necessarily also includes a viscous film-forming material such as carboxymethyl cellulose, hydroxyethyl cellulose, etc.

The aqueous alkaline processing composition may be employed in a variety of ways to develop the exposed light-sensitive material.

However, in a preferred embodiment, the processing composition is confined in a frangible or rupturable container such as disclosed in US. Patents No. 2,543,181 and 2,634,886 issued to Edwin H. Land. The container is so positioned as to be capable, upon rupturing, of forming a substantially uniform layer of the processing composition between the exposed photosensitive element and the reflective layer positioned in superposed relationship thereto. The frangible container may, for example, be positioned between the photosensitive element and the superposed reflective layer, or it may be positioned on the other side of the photosensitive element, in which case the composition, when released from the container, diffuses through the photosensitive element to the reflective layer.

Other means for applying the processing composition will be readily apparent to those skilled in the art and are accordingly within the scope of the invention. For example, it is contemplated that the processing composition or any of the individual components thereof may be encapsulated in minute capsules or the like positioned in a substantially uniform layer' on either side of the photosensitive element. One useful procedure may be to confine the developer in a water-soluble capsule, in which case development is initiated by immersing the film unit in an aqueous alkaline bath to dissolve the capsule, thereby forming the developing composition. Since encapsulation and release of the encapsulated materials by rupturing or breaking, melting, dissolving, etc. the capsule walls are 4 per se old, the use of procedures of this nature will be apparent to those skilled in the art.

The negatives prepared in the foregoing manner have been found to be of good density and contrast. For example, negatives have been prepared having a D of 1.14 and a D of 0.02 to provide a negative of excellent detail having a density range of 1.12.

The abilit to obtain in a single processing step a negative transparency of good detail and contrast is particularly useful in the field of radiography where many roentgenologists or other practitioners are accustomed to viewing negative radiographs and for this reason prefer the negative to the positive radiograph. The present invention therefore provides, in addition to its other advantages, a rapid one-step system for providing a negative X-ray. The importance of this aspect of the invention to the field of medicine and related sciences will be apparent.

It vhas also been found, quite surprisingly, that it is possible by the practice of this invention to provide an image which, in addition to being a negative transparency, can also be viewed by reflected light as a positive reflection print. In other words, it is possible to obtain a single photographic reproduction which may be viewed by transmitted light as a negative or by reflected light as a positive.

Thus, it has been found that, in addition to the etching of the reflective layer, the alkali contacting the reflective layer alters the optical properties of the contacted areas from light-reflective to light-absorptive, so that these areas now absorb light and appear black, whereas the other areas continue to reflect light and appear white. Thus, where the etching is not complete so that substantially all of the reflective material is removed, leaving only the transparent support in the image areas, the image areas may be said to be translucent so that they both absorb and transmit light. This results in a positive reflection print which, due to the etching, may also be viewed by transmitted light as a negative.

The advantages of obtaining a single image which is either a negative or a positive, depending upon the location of the source of viewing light, as well as the advantages of obtaining an image which may be viewed either by transmitted or reflected light will be apparent. These advantages are particularly significant in the field of radiography.

The following example shows by way of illustration and not by way of limitation the preparation of a visible image in accordance with this invention.

Example 1 Aluminum was deposited on a cellulose acetate support by vacuum deposition to provide a polished reflective layer of aluminum having an optical density of about 2.60. A conventional gelatino silver halide emulsion was photoexposed and then developed by spreading between the exposed emulsion and the aluminum sheet in a layer approximately 0.0032 inch thick a processing composition comprising:

Water cc 8289.0 Hydroxyethyl cellulose gm 366.0 Sodium hydroxide gm 212.5 4,6-diamino-ortho cresol gm 270.0

After an imbibition period of two minutes, the aluminum sheet was separated and was found to contain a full tone visible image which, when viewed by reflected light, appeared to be a clear positive image of good density and contrast. When the same image was placed over a standard transparency viewing device and viewed by transmitted light, it appeared to be a clear, sharp negative image of good contrast and detail, having a Dmax, of 1.14 and a Dmin, of 002.

While prints prepared in the manner illustrated in Example 1 are completely satisfactory for most purposes, it

has been found that the imbibition time to obtain a print of comparable density may be lessened by adding to the processing composition a reagent which enhances the ability of the alkaline material to alter the reflective metal layer. Alternatively, a print of greater density for a given time of imbibition may be obtained by the use of such a reagent. S-nitrobenzimidazole has been found to be particularly useful for this purpose.

The following examples illustrate the ability of S-nitrobenzimidazole to enhance image formation.

Example 2 The process of Example 1 was repeated, using the same aluminum layer, gelatino silver halide emulsion and exposure. Development was initiated by spreading between the exposed emulsion and the aluminum sheet in a layer approximately 0.0032 inch thick, the processing composition of Example 1 to which was added 180 gm. of S-nitrobenzimidazole nitrate. After an imbibition period of 90 seconds, the aluminum sheet was separated and was found to contain a full tone image which, when viewed by reflected light, appeared to be a clear positive image of good density and contrast. When the same image was placed over a standard transparency viewing device and viewed by transmitted light, it appeared to be a clear, sharp negative image comparable to the negative image prepared in Example 1.

Example 3 Aluminum was deposited on a cellulose acetate support by vacuum deposition to provide a polished reflective layer of aluminum having an optical density of 3.2. The gelatino silver halide emulsion employed in the preceding examples was photoexposed and then developed by spreading between the exposed emulsion and the alu- Example 4 The process of Example 3 was repeated, adding 270 gm. of S-nitrobenzimidazole nitrate to the processing composition. The period of imbibition in this example was minutes or approximately /2 that of Example 3. A clear sharp negative transparency was formed, having a Dmax, of 2.90 and a D of 1.70 to provide a density range of 1.2. As in the preceding examples, the image could also be viewed by reflected light as a clear positive image.

In the embodiments illustrated in Examples 3 and 4, it will be noted that the aluminum layer was appreciably thicker than the layer employed in Examples 1 and 2. While thicker aluminum layers are preferred in order to obtain a greater D and hence a greater density range, the use of thicker aluminum layers inherently creates certain problems. It will be apparent that, in a given system, the greater the thickness (optical density) of the aluminum layer, the longer the imbibition time necessary to obtain an image of comparable quality. It will also be apparent that the greater the thickness of the aluminum layer in a given system, the more diflicult it is to maintain a constant D due to the inherent difiiculty of etching sufiicient aluminum to transmit light of a given intensity. Thus, while the D obtained in Example 4 was appreciably greater than that in Example 2, the D was also greater, so that the density ranges were about the same. In any event, Examples 3-4 clearly illustrate the ability of S-nitrobenzimidazole to enhance image formation.

In another embodiment of the invention, it has been found that by increasing the alkali concentration in the processing composition, the aforementioned disadvantages inherent in the use of a thicker aluminum layer are obviated. In other words, it has been found that by increasing the alkali concentration, it is possible to obtain the advantages inherent in the use of thicker aluminum layers, e.g., greater D with none of the disadvantages.

The following example illustrates the use of 5-nitrobenzimidazole in processing compositions containing an increased alkali concentration.

Example 5 The process of Example 4 was repeated, using a processing solution comprising:

After an imbibition period of two minutes (as distinguished from the 10 minutes of Example 4 and the 20 minutes of Example 3), the aluminum sheet was separated and was found to contain a full tone visible image which, when viewed by reflected light, appeared to be a clear positive image of good density and contrast. When the same image was placed over a standard transparency viewing device and viewed by transmitted light, it appeared to be a clear negative image of excellent contrast and detail, having a Dmax, of 2.50 and a D of 0.06.

The foregoing example illustrates clearly the ability of increased concentrations of alkali to increase further the ability of S-nitrobenzimidazole to enhance image formation. In illustrative Example 5, the alkali concentration was increased about 15% (based upon the weight of alkali). Smaller increases of alkali concentration enhanced image formation to a lesser extent, while greater amounts were found to be unnecessary. While the amount of alkali employed may vary according to the materials and operating conditions employed, it is within the expected judgment of the skilled worker to ascertain optimum amounts to employ.

It is also within the scope of the invention to provide means for facilitating complete separation of the developed image from the residual processing composition which may contain reagents such as unoxidized developing agent, etc., which may adversely affect the stability of the image, if not removed subsequent to image formation. This means may be a stripping layer which loosely adheres to the metal layer and is stripped away with the residual processing composition and photosensitive element. However, in a preferred embodiment, the separation is simply and efiiciently effected, by a pretreatment of the metal layer at some time prior to development with a material which substantially reduces the adherence of the processing composition to the metal layer subsequent to image formation. One method for accomplishing this result is a pretreatment which alters chemically the surface of the metal layer so that it has less aflinity for the processing composition. In a preferred embodiment, the metal layer is swabbed prior to development with a dilute sodium hydroxide solution which converts the surface of the metal layer to the corresponding oxide, e.g., converts aluminum to aluminum oxide. The processing composition has been found to adhere appreciably less to the oxide than it does to the free metal.

The following example illustrates the aforementioned pretreatment.

Example 6 An aluminum sheet prepared in the manner illustrated in Example 1 was swabbed shortly before development with a solution containing 0.2 gm. of sodium hydroxide in cc. of water. Exposure and development were performed as in Example 1. Upon separation, the image was apparently completely free of the residual processing composition, as distinguished from the process of Example 1 wherein a portion of the processing composition was observed to have adhered to the separated image. In all respects, the quality of the image prepared in this example was comparable to images prepared with no pretreatment, thereby indicating that the pretreatment had not eflect upon the quality of the image.

In addition to the advantages heretofore noted, images formed by the present invention are capable of selective inking to provide a master suitable for obtaining ink reproductions by contacting the master with one or more copy sheets according to conventional techniques.

In other words, it has been found that the unaltered areas of the metal reflective layer are oleophilic, while the altered areas are hydrophilic. This imagewise diiferential permits the image to be employed as a printing master to prepare one or more ink reproductions of the original.

It is therefore possible to prepare negative ink reproductions of the original subject matter by coating the image with an olephilic ink which has a preferential aflinity for the unaltered areas. As is well known in the art of ink reproduction, the selective inking may be facilitated, if desired, by first wetting or swabbing the image with water or an aqueous solution adapted for making ink reproductions, e.g., Platex (trade name of Addressograph- Multigraph Corporation for an aqueous phosphate solution for swabbing lithographic masters prior to inking).

Conversely, it is also possible to prepare positive ink reproductions of the original subject matter by coating the image with a hydrophilic ink which has a preferential affinity for the altered areas. Olephilic and hydrophilic inks useful in the preparation of ink reproductions in accordance with this embodiment of the invention are of course well known in the art.

The following example illustrates the preparation of ink reproductions in accordance with this invention.

Example 7 A print prepared in the manner illustrated in Example 1 was swabbed with Platex and then coated with Multilith SF 10 (trade name of Addressograph-Multigraph Corporation for an oleophilic or greasy black ink for lithography). The inked master was then pressed against a sheet of Ditto copy paper to provide a negative ink reproduction which, while it had a noticeable amount of background inking, was still a clear and sharp negative reproduction of the original subject matter.

The foregoing example illustrates the usefulness of the present invention in such fields as document duplication.

The negative transparencies prepared by the present invention have also been found to be useful in preparing one or more positive prints of good quality by conventional wet processing techniques, e.g., contact printing. Thus, a plurality of positive prints have been prepared by exposing a suitable printing paper, e.g., Kodak Azo Paper, through the negative transparency and developing, fixing and washing in conventional manner.

It is also possible to prepare a polarizing image by employing the light polarizing materials, e.g., the polarizing aluminum sheet material, described and claimed in copending application Ser. No. 187,679 filed Apr. 16, 1962, now Patent No. 3,353,895 in the name of Eugene S. Emerson. As is described with more particularity in the copending application, the light polarizing material may be prepared by vacuum deposition of evaporable materials such as aluminum at a selected or predetermined angle onto a suitable transparent support. A polarizing aluminum sheet material prepared in the manner described in the aforementioned copending application of Eugene S. Emerson may be employed in processes such as described in the foregoing illustrative examples to provide a polarizing image which is also potentially useful in the subsequent preparation of stereoscopic images,

The following example illustrates the use of light polarizing sheet materials.

8 Example 8 A cellulose acetate support was mounted in a highvacuum enclosing tank. The support was adjusted so that an angle of 5 was established between a line extending from a piece of aluminum mounted in a heater within the tank and the plane of the support at a location extending transversely as a line across the support at its center. A vacuum between 10* torr and 10* torr was produced in the tank. The aluminum was heated to its sublimation temperature, namely to approximately 660 C. It was permitted to evaporate and form a deposition on the glass surface for approximately 15 seconds. No special emission bafiie or guide means was employed, so that vaporization was directed, in terms of its vertical dimension, in a somewhat flared or conically shaped manner. This produced a light polarizer which in the area contiguous with the aforesaid center line had a proper density and an essentially neutral transmittance characteristic. The polarizer was removed and was found to have a density (dichroic) ratio of about 15. The polarizing aluminum sheet material prepared in the foregoing manner was substituted for the aluminum sheet material of Example 5. The process of Example 5 was then repeated to provide a visible image which appeared quite similar to the images previously prepared, e.g., the image of Example 5. However, when a second sheet of the polarizing aluminum material was placed between the negative transparency formed in this example and the source of viewing light and the second polarizing material was rotated so that the axis of polarization of the second polarizer was at a angle to the axis of polarization of the transparency, the shadow areas of the image became appreciably darker.

The concept of forming polarizing images described above and illustrated in Example 8 is claimed in copending application Ser. No. 297,657 filed concurently in the name of Meroe M. Morse.

From the foregoing description and illustrative examples, it will be seen that the present invention provides a rapid one-step system for preparing negative transparencies which in one embodiment may also be viewed by reflected light as a positive. The invention is particularly adaptable to the field of radiography since a lightsensitive silver halide emulsion may be exposed to penetrating ionizing radiation, e.g., X-rays, in conventional manner and the thus exposed emulsion may then be employed by the present invention to provide a radiograph which is a negative transparency and, in one embodiment, may also be viewed by reflected light as a positive radiograph. The images prepared by the present invention may also be used as inking masters for the production of ink copies and are also useful in the preparation of positive copies by conventional techniques, e.g., contact printing.

While aluminum is the preferred material for forming the reflective layer, it will be appreciated that various other metals are within the scope of the invention, provided, of course, that they are reactive with alkali in the manner heretofore described.

It will likewise be appreciated that where a transparency and the advantages resulting therefrom are not desired, e.g., when the prime objective is to provide an inking master, the support for the deposition of metal need not be transparent. It is therefore to be expressly understood that the particular support employed in the practice of this invention is not critical and may be either opaque or transparent depending upon the objectives of the practitioner.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A photographic process for preparing an image viewable alternatively either as a positive reproduction or as a negative reproduction which comprises developing an exposed photosensitive element with an aqueous alkaline processing composition; as a product of development, exhausting the alkaline material in said processing composition in areas of exposure; contacting a superposed sheet material comprising a thin reflective metal layer on a substantially transparent support with unexhausted alkali; allowing said alkaline material to contact said sheet material for a time suflicient to provide an imagewise removal of a portion of said metal but insufficent to remove substantially all of said metal in said areas, said image areas containing the remainder of said metal being translucent whereby they both absorb and transmit light; and thereafter, separating said sheet material to provide an image which is viewable by transmitted light as a negative image of the subject matter to which said photosensitive element has been exposed, said image also being viewable by reflected light as a positive image of said subject matter.

2. A process as defined in claim 1 wherein said metal is aluminum.

3. A process as defined in claim 2 wherein said aluminum layer is applied on said transparent support by vacuum deposition, the optical density of said reflective layer of aluminum being from about 0.75 to about 3.5.

4. A process as defined in claim 1 wherein said processing composition includes a reagent for lowering the contacting time by said composition necessary to form said image.

5. A process as defined in claim 4 wherein said reagent is S-nitrobenzimidazole.

6. A process as defined in claim 1 including the step of coating said sheet material, at some time subsequent to development and image formation, with an ink which will preferentially wet one of said image areas and non-image areas, whereby to form a printing master.

7. A process as defined in claim 1 including the step of pressing said inked master against at least one copy sheet to provide an inked reproduction of said image.

8. A process for preparing radiographs viewable alternatively either as a positive or as a negative radiograph which comprises exposing a photosensitive element to penetrating ionizing radiation to form a developable image; developing said exposed element with an aqueous alkaline processing composition; as a product of develop ment exhausting the alkaline material in said processing composition in areas of exposure; contacting a superposed sheet material comprising a thin reflective metal layer on a substantially transparent support with unexhausted alkali; allowing said alkaline material to contact said sheet material for a time suflicient to provide an imagewise removal of a portion of said metal in terms of unexposed areas of said emulsion but insufficient to remove substantially all of said metal in said area-s, said image areas containing the remainder of said metal being translucent whereby said areas both absorb and transmit light; and thereafter separating said material to provide a radiograph which is viewable by transmitted light as a negative radiograph, said radiograph also being viewable by reflected light as a positive radiograph.

References Cited UNITED STATES PATENTS 804,038 11/1905 Pifer 96-79 2,384,593 9/1945 Bean 96-109 XR 804,029 11/1905 Pifer 96-79 2,647,055 7/1953 Land 96-29 2,997,390 8/1961 Land 96-29 3,114,833 12/1963 Fine 96-2 3,163,554 12/1964 GesSler 117-45 3,185,841 5/1965 Land 96-96 X 3,186,842 5/1965 De Haes et a1. 96-29 3,189,454 6/1965 Luckey et a1. 96-29 X 3,222,175 12/1965 Rasch 96-29 X NORMAN G. TOR'CHIN, Primary Examiner. JACK P. BRAMMER, Assistant Examiner. 

